Abstract: Abstract: Along with the development of modern natural gas pipeline networks in the direction of large-scale, complex and networked features, the challenges of accurately and rapidly analyzing the hydraulic and thermal change processes of the pipeline networks as well as real-time monitoring the equipment status have become increasingly severe. To ensure the safety and reliability of the operation of natural gas pipeline networks and deeply explore the variation mechanism of their operating conditions, this paper focuses on large-scale natural gas pipeline networks and successfully develops an online simulation software for large-scale natural gas pipeline networks based on the partitioned adaptive iterative state estimation algorithm. After its deployment and going online, this software can meet the online simulation requirements of large and complex natural gas pipeline networks at the scale of 20,000 kilometers. Taking a regional pipeline network in China with a scale of 20,000 kilometers as an example, by comparing and validating with the measured data of SCADA, the maximum error of the predicted values of key process parameters such as pressure, flow rate and temperature along the pipeline network by this software is controlled within 5%. This software exhibits outstanding robustness against complex situations such as missing real-time data and anomalies, and can automatically complete the correction of measured data at the model and data levels. The results confirm that this software satisfies the requirements of industrial-grade software in terms of applicable scale, computational efficiency and accuracy, and can lay a solid technical foundation and provide strong technical support for the intelligent operation and maintenance of natural gas pipeline networks and the digital transformation of the energy industry.